Guthrie, a nod to John or Mona Lisa Guthrie. Before the Resonance Cascade, the Black Mesa Announcement System in Sector C mentions him in the message "Dr. Guthrie, report to Inspection Lab 6 immediately.". After the Resonance Cascade, his locker is open; inside can be found two Glock 17 magazines on what appears to be an ammo box, as well as a US flag.

Louis Donaldson, a scientist involved in the research of creatures found on Xen prior to the Black Mesa Incident. During his work, he became the discoverer of the Barnacle creature, but unfortunately also its first victim. The Barnacle's full name, Cirripedia donaldsonia, was subsequently named after him.[3] His name is a nod to Louise Donaldson, thanked in the Half-Life credits.

S. Jones, a nod to Steven Jones, he is a scientist whose corpse is seen in Opposing Force, lying near his desk on which is name tag is seen. He was presumably working on the Displacer Cannon with his nearby colleague S. Reardon, also dead. He also appears to own or have been using a Glock 17, as one is seen on his desk.

Smithers, scientist who appears in the Half-Life level Blast Pit. During the Black Mesa Incident, Silo D-02's power generator has to be started up to defeat the Tentacles in Silo D-01, and Smithers is sent to restart it. It is likely he encounters some Xen aliens on the way there, because instead of restarting the generator, he decides to hide on top of the generator until the crisis ends. Having failed to start the generator and failed to return, Smithers' colleague met below by Freeman assumes he has been killed and states he did not attempt to restart the generator himself. Later, Gordon comes down to restart the generator. Upon stepping onto the device, he encounters Smithers, who refuses to move until the situation drastically improves. Freeman restarts the generator and leaves, while Smither's fate remains unknown.

S. Reardon, a nod to Sean Reardon, he is a scientist whose corpse is seen in Opposing Force, lying near his desk on which is name tag is seen. He was presumably working on the Displacer Cannon with his nearby colleague S. Jones, also dead. In Blue Shift, the same name tag can be found on the desk in the office where Harold has retreated.

Tolman, a scientist who worked with Doctors Rosenberg and Keller at the time of the Resonance Cascade. During the experiment on GG-3883, he was to power up the secondary magnetic charges. He was killed by the surge of destruction immediately following the incident. Rosenberg was frightened and alerted by his death, but Keller brushed it off in the face of the disaster.

Van Buren, a nod to Bill Van Buren, he is a scientist who occupied an office in Sector D's Administration Offices. Left of the office door is a sign with his name, with "Diplomatic Relations" under it. When Gordon Freeman reaches the office, a scientist jumps through the window; this may be him. Inside the office are a shotgun, ammo for it and two Medkits.